Amputee Gets a Shot at the Olympics

Last week, Oscar Pistorius, a South African Paralympics
runner, was granted the chance to fulfill his lifelong dream of competing in
the Olympics by the Court of Arbitration for Sports (CAS), in Lausanne, Switzerland.
The court upheld the appeal filed by Pistorius against the decision made on
January 14 by the International Association of Athletics Federations (IAAF) that banned the “blade runner”
from competing against able-bodied athletes. The CAS
ruled that the IAAF did not provide “sufficient evidence of any metabolic
advantage … [or sufficient evidence] that the biomechanical effects of
using this particular prosthetic device gives Oscar Pistorius an advantage over
other athletes not using the device.”

Augmented humans: Hugh Herr, an MIT Media Lab professor and director of the Biomechatronics Group, led a team of researchers who evaluated the scientific validity of an IAAF study used to ban Oscar Pistorius, a Paralympics runner, from competing in able-bodied competitions.

Pistorius is a double amputee who competes on J-shaped,
carbon-fiber, Cheetah Flex-Foot prosthetics made by the Icelandic company Össur. After Pistorius performed
well in an international able-bodied event in 2007, suspicion arose among
members of the IAAF that his Cheetah prosthetics may give him an unfair
advantage. Immediately, the institution placed a ban on using “technical
devices,” such as wheels and springs, in competition, and it decided to
individually review Pistorius’s case.

The IAAF conducted a two-day scientific study, led by German
professor Gert-Peter Brüggemann, of the prostheses. Based on the resulting
data, the IAAF concluded that Pistorius indeed has an unfair advantage over
able-bodied athletes, claiming that he uses 25 percent less energy than they do
to compete.

Astounded by such allegations, Pistorius’s lawyers turned to
MIT professor Hugh Herr
and asked that he assess the scientific validity of the IAAF’s study. Herr, the
director of the Biomechatronics Group in the MIT Media Lab, and also an
associate professor in the MIT-Harvard Division of Health
Sciences and Technology, assembled a team that included experts in biomechanics
and physiology from six universities to evaluate the scientific evidence.

Technology
Review sat down with Herr and asked him to explain the scientific flaws
that the team of researchers found in the IAAF study, as well as the broader
implications of the CAS’s ruling.

Technology Review: What were the claims made by the IAAF in its
scientific report that you were tasked with assessing?

Hugh Herr: The
first claim made by the IAAF was related to the metabolic energy required of
Oscar to run. They claimed that Oscar, because of his Cheetah prostheses, was
able to run at sprinting speeds with 25 percent less energy. In the second
claim, the IAAF said the Cheetah prostheses release a greater amount of energy
than the human ankle-foot complex in sprint speeds, and that that, in fact,
introduces an artificial advantage to Oscar.

TR: In regards to the first claim, how did the IAAF come to
that conclusion, and what scientific evidence did you use to refute that claim?

HH: At sprinting
speeds, the body uses two sources of energy: aerobic and anaerobic. The problem
is that you can measure one energy source but not the other. Anaerobic energy
cannot be quantified by anyone–not here in the U.S.,
not in Germany;
it simply can’t be precisely quantified. The IAAF claimed that it could be
quantified, and they put a precise number on it: 25 percent energetic advantage
at 400-meter-race speeds. This is deeply flawed because it can’t be quantified
at those speeds. No one can assess quantitatively whether there is an advantage
or disadvantage.

TR: Then how did the IAAF quantify the anaerobic energy source
in order to come to such a conclusion?

HH: They took
blood lactate measures. But again, if one is schooled in the recent scientific
understanding of anaerobic metabolism, one concludes that by simply taking
blood lactate measures, one cannot quantify anaerobic capacity.

At slower running speeds, the aerobic component can be
measured by monitoring how much oxygen a person consumes and how much carbon
dioxide is released. What we did is, we performed an energetic test at slower
running speeds where one can quantitatively measure the total amount of energy
required to run, because at that critical speed and below, the aerobic energy supply
forms the entirety of the energy source. We measured Oscar and other elite
athletes with intact legs at that speed and below, and we found no significant
difference.

If the IAAF would have had their study peer-reviewed before
deciding to ban Oscar, they would have found this out.

TR: In the second claim, the IAAF said that the Cheetah
prosthetics returned more energy than the human ankle-foot joint. How was that
evaluated, and why do you believe the ruling is flawed?

HH: The IAAF
looked at the net mechanical energy of the human ankle-foot joint at
400-meter-race speeds and found that the ankle absorbs more mechanical energy
than it releases. That is fine–they used standard procedure to look at ankle
torque and power–but they then concluded that the body dissipates that energy.
There is so much energy that is absorbed, and so much that is released, and
they assumed the difference the body just throws out as heat. That is a highly
questionable theory because typically the body does not throw out enormous
amounts of energy as heat unless a person is continually going down hill where
the body must dissipate energy. What might be an alterative hypothesis … is
that not all of the energy is lost, and some of it is transferred to the knee.
In our body, we have muscles that span multiple joints; for example, the calf
muscle … goes past the ankle and the knee. Biomechanically, we know that
one purpose of such muscles is so that the body can transfer energy across
joints. The IAAF did not explore this possibility, but instead put forth a
theory that the body is throwing all that energy out. They stated as fact that
the human intact leg has a disadvantage compared to the Cheetah prosthesis,
which is a spring, because it absorbed more energy than [it] released, and the
difference is dissipated as heat.

TR: If the IAAF had assumed that the absorbed energy was
transferred instead of dissipated as heat, would the energy measurements
between the ankle-foot joint and the prosthetic have been similar?

HH: In terms of
how much energy would be stored, yes. This also assumes that their very premise
is valid, and their premise is that whether the ankle absorbs more than it
releases or releases more than it absorbs at those speeds is the critical
determinant of who wins the 400 meter race, which is highly suspect.

Peter Weyand [a member of Herr’s research team and the
director of the Locomotion Laboratory at Rice University] studies sprinting and
what determines peak running speed, and he found that really fast people
generate very high forces on the ground, and they do so very fast. Slower
people are not able to generate high forces. One important feature of running
fast is not what the joints are doing but the overall leg ability to generate
high forces on the ground for a very short time. Now, we found that, and Dr. Brüggemann
found that Oscar’s ground forces seem to be slightly lower than an athlete’s
with legs. This suggests that perhaps he might be force limited because his
prosthesis is just a spring, and he cannot generate the high forces an intact
leg can.

Now, what our research is saying is not that [the IAAF
study’s] data are flawed, but that it is the interpretation of the data we
found questionable. The burden of proof is with the IAAF. If they want to ban
Oscar and perhaps all amputees that use Cheetah prostheses, they need to show
scientifically that it does show an overall advantage in the 400 meter race.
Our point is that this is an important matter, and one needs to be very careful
with the science. Therefore, there needs to be a high level of certainty of
what biomechanically and energetically is going on in terms of the prosthetic
effect. Brüggemann did a select set of experiments, and with that data, he did
make certain scientific claims that we don’t agree with. We don’t agree with
this interpretation of the data, but then beyond that, the IAAF made a much
broader statement. They said that Pistorius has an overall advantage in the 400
meter race.

TR: Did your research team conduct any further studies to show
either that the IAAF’s scientific evaluation was flawed or that Pistorius does
not have an advantage?

HH: We did one
measure that was not directly related to the claims made by the IAAF. If you
take a sprint athlete, and at a particular running speed you measure the time
duration they can maintain that speed, and then you change the speed and
measure the new time duration and so on, you get a speed-duration curve. At
really, really fast speeds, the person can take, like, 10 steps and maintain
that speed for a short duration. As you lower the speed, the duration gets
longer and longer. Sprint athletes with intact limbs all fall on a very
standard line. We thought if Oscar is artificially augmented, he would not fall
on that speed-duration curve. We did the test, and he falls right on the curve,
which is an indication that he fatigues in the same manner as able-bodied
sprinters.

TR: What are the broader implications of the CAS ruling?

HH: Oscar will be
given the opportunity to qualify for IAAF-sanctioned events. But broadly, it
will be progress in the overall initiative to fully integrate people with
disabilities in society. Some people in the world witness an extraordinary
athlete that has artificial legs or arms … and they immediately think that
cannot be so–disabled people cannot be this good at something. It never occurs
to some people that Oscar may be a remarkable athlete. They think he has to be
cheating.

There is so much to learn about how the human body works
and, in addition, how the body is affected by a wearable device, like a shoe or
prosthesis. The day that there is a prosthesis that outperforms an intact limb
using any single metric–whether it is to jump high or to manipulate
something–will indeed be a very exciting day.